Synthesis of 4,4-Dihydrodithienosilole and Its Unexpected

May 11, 2017 - 4,4-Dihydrodithienosilole (DTSH2) was isolated from a mixture of 3,3′-dibromobithiophene, n-BuLi, and H2SiCl2 and was fully character...
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Synthesis of 4,4-Dihydrodithienosilole and Its Unexpected Cyclodimerization Catalyzed by Ni and Pt Complexes Makoto Tanabe,† Toshihiro Hagio,† Kohtaro Osakada,*,† Masashi Nakamura,‡ Yuya Hayashi,‡ and Joji Ohshita‡ †

Laboratory for Chemistry and Life Science, Tokyo Institute of Technology, 4259-R1-3 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan ‡ Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan S Supporting Information *

ABSTRACT: 4,4-Dihydrodithienosilole (DTSH2) was isolated from a mixture of 3,3′-dibromobithiophene, n-BuLi, and H2SiCl2 and was fully characterized. The reaction of DTSH2 with a Pt(0) complex, prepared in situ from [Pt(PCy3)2] and DPPE (1,2bis(diphenylphosphino)ethane), produced a bis(silyl)platinum complex [Pt(DTSH)2(dppe)] (1) with two hydrodithienosilole ligands. DTSH2 undergoes cyclodimerization accompanied by skeletal rearrangement to afford a cis-fused bicyclic compound (2) upon heating the solution in the presence of a catalytic amount of 1 or [Ni(PPh3)4]. The product has a Si−Si bond that bridges two Si atoms, separated by 2.309(1) Å. Bicyclic disilane 2 forms the Pt complex (3) with two Si ligands and retaining the 10-membered macrocycle ligand via the Si−Si bond cleavage.

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INTRODUCTION Silole derivatives with a fused-ring system, such as dibenzosiloles (DBSs)1 and dithienosiloles (DTSs)2 (Chart 1), have

lole and its polymers and copolymers, however, has not been reported to date. In this paper, we report the synthesis and properties of DTSH2 and its cyclodimerization accompanied by skeletal rearrangement catalyzed by Ni and Pt complexes.

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Chart 1. Silole Derivatives

RESULTS AND DISCUSSION Addition of H2SiCl2 to 3,3′-dilithiobithiophene, obtained in situ from the reaction of n-BuLi with 3,3′-dibromobithiophene, afforded 4,4-dihydrodithienosilole (DTSH2) in 86% yield. The 1 H NMR spectrum contains a SiH signal at δ 4.53 with 1JSiH = 215 Hz; a 29Si{1H} NMR signal is observed at δ −56.0 (SiMe4 as an external standard). DTSH2 further reacted with [Pt(PCy3)2] and DPPE (1,2-bis(diphenylphosphino)ethane) at a 2:1:1 ratio to afford the Pt(II) complex with two hydrodithienosilole ligands, [Pt(DTSH)2(dppe)] (1, 42%), as shown in eq 1.The 31P{1H} NMR signal of 1 revealed a typical 1 JPtP value of bis(silyl)platinum complexes with a cis structure (1727 Hz), similar to that of [Pt(SiPh2H)2(dppe)] (1515 Hz).13 The 1H NMR spectrum of 1 showed a Si−H signal at δ 6.33 coupled with 29Si, 31P, and 195Pt nuclei (3JPH = 7.0 Hz, 2 JPtH = 77 Hz, and 1JSiH = 187 Hz). Heating a toluene solution of DTSH2 in the presence of a catalytic amount of 1 (5 mol %) at 90 °C resulted in the formation of bicyclocompound 2 composed of two fused dithienocyclohexadiene rings that are bridged by a disilanylene group in 77% yield (eq 2).

attracted attention as materials of π-conjugated oligomers and polymers.3−5 The π-conjugated systems with silole groups have enhanced the luminescent and electron-transporting properties because of the high electron affinity of the silole-based compounds.6 Poly(1,1-silole)s7,8 and poly(1,1-dibenzosilole)s9,10 are composed of a silicon backbone and possess a structure with σ−σ* delocalization along the main chain and σ−π* conjugation at each silole ring. Ohshita et al. reported that 4,4-dichlorodithienogermole derivatives reacted with sodium to produce poly(dithienogermole)s11 and that their reduction yields 4,4dihydrodithienogermole (DTGH2).12 4,4-Dihydrodithienosilole (DTSH2), the parent compound of 4,4-dialkyldithienosi© XXXX American Chemical Society

Received: March 6, 2017

A

DOI: 10.1021/acs.organomet.7b00177 Organometallics XXXX, XXX, XXX−XXX

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almost coplanar with twisting angles of 6.40 and 16.37° (Figure 1b). Ohshita reported that the reaction of 1,1,2,2-tetrachloro1,2-dialkyldisilane with 3,3′-dilithiobithiophene derivatives produced similar bicyclic disilanes with the Me or i-Bu substituents at the Si atom and that the trans isomer is formed preferentially.14 The reaction mixture from eq 2 does not contain any trans isomer 2′. The Si−Si bond of 2 (2.309(1) Å) is slightly shorter than those of disilanylene-bridged bithiophenes (2.320(3) and 2.338(2) Å).2b The molecules have both an intermolecular π-stacking interaction between two bithiophene groups with distances of 3.453−3.568 Å and a short C··· C contact between the vinylene carbons of the other bithiophene groups (3.407 and 3.500 Å). Thus, a stack of alternating bithiophene rings along the c axis of the crystal cell is observed, as shown in Figure 1c. Density functional theory (DFT) calculations for the cis geometry of 2 (MPWB95/631G(d,p) level) revealed higher thermodynamic stability than those for the trans conformer of 2′ (ΔG = 12.8 kcal mol−1). The low-lying LUMO energy level is attributed to the extended bonding interaction between the σ* orbitals of the Si−H and Si−C bonds and the π* orbitals of the butadiene moieties (σ*−π* interaction). The 29Si NMR signal of 2 at δ −70.1 was shifted upfield relative to that of DTSH2 (δ −56.0) owing to the formation of tertiary Si atoms. The UV−vis absorption and fluorescence spectra of DTSH2 and 2 in THF are shown in Figure 2, and the results are

[Ni(PPh3)4] (1 mol %) also catalyzed the reaction of DTSH2 at room temperature to produce 2 in 34% yield. [Ni(dmpe)2] (dmpe = 1,2-bis(dimethylphosphino)ethane) converted DTSH2 into a mixture of 2 and many uncharacterized compounds. A similar reaction of 2,6-bis(trimethylsilyl)-4,4dihydrodithienosilole catalyzed by [Ni(PPh3)4] yielded the corresponding dimer in a higher yield (59%). This was in contrast to the reaction of silafluorene in the presence of a catalytic amount of [Ni(dmpe)2] to form the oligomers and insoluble polymers with a Si−Si backbone.10 Figure 1a shows the molecular structure of 2 determined by X-ray crystallography. The two fused six-membered rings of 2 are bonded via a Si−Si bond and have two Si−H bonds with a cis geometry. Two thiophene rings combined with a C−C single bond are

Figure 2. (a) UV−vis absorption and (b) photoluminescence spectra of (i) DTSH2 in THF, (ii) 2 in THF, and (iii) 2 in the solid state. The concentration for (a) was 1.0 × 10−4 M and that for (b) was 1.0 × 10−5 M. The excitation wavelengths of DTSH2 and 2 were 337 and 336 nm, respectively.

summarized in Table 1. The absorption and emission bands of DTSH2 (λmax = 337 nm) are at shorter wavelengths than those for 4,4-diphenyldithienosilole (DTSPh2; λmax = 356 nm). The substituents on the Si atoms affect the electronic states of the dithienosilole rings. The absorption and emission bands of 2 (λmax = 336 nm, λem = 418 nm) are similar to those of DTSH2 (λmax = 337 nm, λem = 411 nm) except for a shoulder peak at 360 nm. The reported dimer, dDTSMe, also exhibited a

Figure 1. Thermal ellipsoids (50% probability) of 2 viewed from (a) the side and (b) the top of the Si−Si bond. Selected bond distances (Å) and angles (deg): Si1−Si2 2.309(1), Si1−C1 1.870(3), Si1−C9 1.870(3), Si2−C5 1.875(3), Si2−C13 1.859(3), C1−Si1−C9 112.3(1), C1−Si1−Si2 104.9(1), C9−Si1−Si2 103.8(1), C5−Si2− C13 108.8(1), C5−Si2−Si1 103.2(1), C13−Si2−Si1 105.2(1). (c) Packing structure of 2. B

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by immediate oxidative addition of the starting material or the product by the reaction. In Scheme 1, we summarize a plausible reaction pathway for the formation of 2 from DTSH2 catalyzed by the Pt complex.

Table 1. Optical Data for DTSH2 and its Dimer 2 photoluminescencea

UV−vis abs compd DTSH2 DTSPh2b 2 dDTSMec

λmax/nm (ε/M

−1

−1 a

cm )

337 (7595) 356 (6080) 336 (8724) 360 (sh) 348, 376 (sh)

λem/nm 411 420 418 (447)d

ΦF/% 36

Scheme 1. Plausible Mechanism of Catalytic Cyclodimerization of DTSH2a

7 (3)d

a

In THF. bRef 2a. cRef 14. dThe values in parentheses were measured in the solid state.

shoulder at 376 nm.14 They may be assigned to a vibrational structure, although support by theoretical calculations has not been obtained at present. The quantum yield (ΦF) of 2 (ΦF = 7%) was significantly lower than that of DTSH2 (ΦF = 36%). The enhanced quenching in solution may be related to conformational flexibility of the disilacyclohexadiene ring.15 To elucidate the pathway for eq 2, further studies were undertaken. The 31P{1H} NMR spectrum of the reaction mixture after 1 h shows a signal for complex 1, but the observed major Pt-containing species after 9 h corresponds to a single signal at δ 59.2 with JPtP = 1678 Hz. The 31P{1H} NMR results are identical with those obtained as the major product from a stoichiometric reaction of isolated 2 with a mixture of [Pt(PCy3)2] and DPPE (1:1:1) at 90 °C (eq 3). The common

product of both of the reactions is assigned as a bis(silyl) platinum complex [Pt(dDTSH)(dppe)] (3, 43%) with a macrocyclic Si ligand. The 29Si{1H} NMR spectrum contains a signal at δ −23.1 (2JPSi = 144 and 4 Hz). The coupling constants are similar to those of 1 (2JPSi = 152 and 14 Hz) and suggest the formation of bis(silyl)platinum complex with a cis structure. The 1H NMR signals corresponding to complex 3 are at δ 6.85 and 6.73 (3JHH = 5 Hz) due to the thienyl hydrogens and at δ 5.23 (3JPH = 11, 26 Hz, 2JPtH = 15 Hz, and 1JSiH = 179 Hz) due to the SiH hydrogen. The 2JPtH value of 3 is similar to that of [{Pt(PEt3)2}{1,2-(H2Si)2C6H4}] (δ 5.31, 2JPtH = 12 Hz)16 and is much smaller than that of 1 (2JPtH = 77 Hz). The results can be attributed to the different orientation of the Si− H bonds between 1 and 3. The Si−H bond of complex 3 should be oriented toward the phenyl rings of DPPE due to the double-chelating coordination of the Si-ligand, while complex 1 has the structure with the Si−H bond oriented to the opposite side of the Pt center. DFT calculations revealed that complexes 1 and 3 have the different orientation of the Si−H bonds as discussed above. Long distances between the two Si atoms (1: 3.1065 Å, 3: 3.09398 Å) and small Wiberg bond indices (1: 0.1783, 3: 0.1698) as well as Pt−Si bonds (1: 2.3792, 2.3794 Å, 3: 2.3643, 2.3647 Å) were noted in the optimized structures. These results indicate that complex 3 has no chemical bond between the Si centers, similar to complex 1, and that complex 3 was formed via oxidative addition of disilane 2 to the Pt(0) center. Complex 3 was estimated to be more stable than 1 by 6.5 kcal mol−1, which renders the catalytic reaction in eq 2 smoothly. The catalysis involves elimination of compound 2, which is followed

a

(a) Initial period; (b) late period.

As shown in Scheme 1a, the reaction at an early stage involves (i) formation of 1 with two silyl ligands, (ii) intramolecular rearrangement to cleave the Si−C bond of the silole ring, which has been hardly reported in the literature,17 and to form a 10membered bis(silyl) ligand, and (iii) elimination of the product accompanied by oxidative addition of a new substrate molecule. The reaction at a late period proceeds as shown in Scheme 1b. Complex 1 is converted to 3′ (iv), similar to Scheme 1a, and elimination of 2 leads to the formation of coordinatively unsaturated Pt(dppe) (v), which undergoes oxidative addition of the Si−Si bond to the Pt(0) center from the other side of the disilane molecule to yield intermediate 3 (vi), which is stable under the conditions and exists in the resting state in the catalytic cycle. An associative reaction of DTSH2 with the intermediate eliminates product 2 and regenerates complex 1 (vii). At an early stage of the reaction (1 h), the former reaction occurs more rapidly because of a large amount of remaining DTSH2 in the reaction mixture, but after 9 h, oxidative addition C

DOI: 10.1021/acs.organomet.7b00177 Organometallics XXXX, XXX, XXX−XXX

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Organometallics of product 2 becomes dominant owing to consumption of DTSH2. The reaction pathways are consistent with the result of monitoring 31P{ 1H} NMR spectra in the Pt-catalyzed dimerization. Scheme 2 shows the geometry of the concerted bond activation and the formation reactions in the catalytic cycle. Scheme 2. Concerted Activation and Formation During Catalysis

Figure 3. Thermal ellipsoids (50% probability) of 4. Atoms with asterisks are crystallographically equivalent to those having the same number without asterisks. The bithiophene ring was disordered. Selected bond distances (Å) and angles (deg): Pt−P1 2.290(2), Pt− P2 2.279(2), Pt−Si 2.373(2), Si···Si* 2.692(4), Pt···Pt* 3.9086(9), P1−Pt−P2 86.59(7), Si−Pt−Si* 69.11(8), P1−Pt−Si 165.10(7), P1− Pt−Si* 104.02(7).

Activation of two Si−C bonds and Pt−Si bonds occurs concomitantly with formation of a Si−Si bond, as well as new Si−C bonds between a Si atom and a thienylene carbon of another dithienosilole group. Steric repulsion of 3′ between the thienyl ring and the DPPE ligand promotes elimination of the product from the Pt(II) intermediate. The Pt(0) species formed is unstable and undergoes oxidative-addition of DTSH2 or 2 rapidly. Heating complex 1 at 60 °C without addition of DTSH2 or 2 produced not only complex 3 formed via cyclodimerization of the ligand and its recoordination but also a diplatinum complex having two bridging silylene ligands [{Pt(dppe)}2(μ-DTS)2] (4, 24%) as a major product (eq 4). The 1H NMR spectrum

the stoichiometric and catalytic reactions can be explained as follows. Complex 4 is formed in eq 4 via generation of the Pt(dppe) intermediate by the elimination of 2 and the dehydrogenative coupling of the coordinatively unsaturated intermediate and unreacted 1. In summary, we succeeded in isolating 4,4-dihydrodithienosilole and discovered its uncommon cyclodimerization accompanied by skeletal rearrangement. The product has a cis-fused bicyclic structure formed by concerted activation of the bonds of the ligand as well as the Pt−Si bond and simultaneous formation of the Si−C bonds between the dithienosilole rings. The results are contrasted with the reactions of silafluorenes with Ni complex in our previous studies, where simple polymerizations of the molecules via Si− Si bond formation proceeds smoothly.10

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EXPERIMENTAL SECTION

General Procedures. All manipulations were carried out using standard Schlenk line techniques under an atmosphere of argon or nitrogen or in a nitrogen-filled glovebox (Miwa MFG). Hexane, toluene, and tetrahydrofuran (THF) were purified by using a Grubbstype solvent purification system (Glass Contour).20 1H, 13C{1H}, 29 Si{1H}, and 31P{1H} NMR spectra were recorded on a Bruker Biospin Avance III 400 MHz and Avance III HD 500 MHz NMR spectrometers. The chemical shifts in 1H and 13C{1H} NMR spectra were referenced to the residual peaks of the solvents used.21 The peak positions of the 29Si{1H} and 31P{1H} NMR spectra were referenced to external SiMe4 (δ 0) and 85% H3PO4 (δ 0) in deuterated solvents. IR spectra were recorded on a JASCO FTIR-4100 spectrometer. UV− vis absorption and photoluminescence spectra of DTSH2 and 2 in THF and in the solid state were recorded using Hitachi U-3210 spectrometers and HORIBA FluoroMax-4 spectrophotometers, respectively. Elemental analysis was performed using a J-science JM10 or a Yanaco HSU-20 autorecorder. HRMS (ESI) measurement was carried out with a Bruker micrOTOF II (eluent: CH2Cl2). The compounds 3,3′-dibromo-2,2′-bithiophene (TCI), 3,3′-dibromo-5,5′bis(trimethylsilyl)-2,2′-bithiophene (Aldrich), n-BuLi in hexane (Kanto Chemical), 10% H2SiCl2/N2 (Taiyo Nissan Sanso), and 1,2bis(diphenylphosphino)ethane (Aldrich) were used without any purification. [Pt(PCy3)2]22 and [Ni(PPh3)4]23 were prepared according to the literature. Caution! H2SiCl2 is f lammable and reacts with atmospheric water to release HCl gas, which is corrosive to tissue. All experiments should be carried out in a well-ventilated hood.

after heating for 102 h displayed the CH signals of 3 and 4 in 1.0:1.8 ratio. A similar dimerization of the bis(silyl)palladium complex [Pd(SiPh2H)2(dmpe)] at 60 °C was reported to afford [{Pd(dmpe)}2(μ-SiPh2)2] in a low yield, accompanied by elimination of H2SiPh2.18 The platinum complex with two bridging DTS ligands, 4 (30%), was independently prepared from the reaction of DTSH2 with [Pt(PCy3)2] in the presence of DPPE at 1:1:1 ratio and 60 °C for 45 h. The molecule of 4 has a rhombus Pt2Si2 core with a short Si···Si contact (2.692(4) Å), as revealed by X-ray crystallography (Figure 3), which is within the range of the corresponding bonds of the diplatinum analogues, (2.554(8)−2.718(2) Å).19 The bithiophene rings with a planar configuration are sandwiched between two Ph rings of DPPE ligands at short distances of 3.5−3.8 Å, indicating the presence of intramolecular π-stacking interaction. Formation of 4 in addition to 3 by heating complex 1 suggests that the reactions (ii) and (iii) in Scheme 1a require the addition of DTSH2 to intermediate 1. The consistencies of D

DOI: 10.1021/acs.organomet.7b00177 Organometallics XXXX, XXX, XXX−XXX

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0.24 (s, 18H, SiCH3, 2JSiH = 7 Hz). 13C{1H} NMR (126 MHz, C6D6, rt): δ 156.6 (Cq-Si), 141.9 (α-Cq or SiCH3), 137.3 (α-Cq or SiCH3), 137.2 (CH), − 0.53 (SiCH3). 29Si{1H} NMR (99 MHz, C6D6, rt): δ −7.04 (SiCH3), − 57.8 (Si-silole). IR (KBr): 2156 cm−1 (νSiH). Ni-Catalyzed Dimerization of DTSH2-SiMe3. The catalytic dimerization was similar to that of 2. The reaction of DTSH2-SiMe3 (100 mg, 0.30 mmol) in the presence of 1 mol % [Ni(PPh3)4] (3.3 mg, 3.0 μmol) in toluene (1 mL) at room temperature for 18 h was performed to produce the corresponding dimer in 59% yield (60 mg, 0.089 mmol). HRMS (ESI) calcd for C28H42S4Si6 [M + Na]+ = 697.0678, found m/z = 697.0682. 1H NMR (500 MHz, C6D6, rt): δ 7.54 (s, 4H, CH), 5.30 (s, 2H, SiH, 1JSiH = 212 Hz), 0.20 (s, 36H, SiCH3). 13C{1H} NMR (126 MHz, C6D6, rt): δ 152.3 (Cq-Si), 141.5 (α-Cq), 140.1 (C-TMS), 126.3 (CH), − 0.54 (SiCH3). 29Si{1H} NMR (99 MHz, C6D6, rt): δ −6.80 (SiCH3), − 70.1 (Si-silole). IR (KBr): 2133 cm−1 (νSiH). Preparation of [Pt(dDTSH)(dppe)] (3). To a toluene solution (6 mL) of [Pt(PCy3)2] (98 mg, 0.13 mmol) were added an equimolar amount of DPPE (51 mg, 0.13 mmol) and 2 (50 mg, 0.13 mmol). The reaction mixture was stirred at 90 °C for 19 h to produce a red solution. The solvent was removed under reduced pressure to give a solid, which was washed with hexane (4 mL × 3) and dried in vacuo to give 3 as a brown solid (55 mg, 43%). HRMS (ESI) calcd for C42H34P2PtS4Si2 [M + Na]+ = 1002.0097, found m/z = 1002.0074. 1H NMR (500 MHz, C6D6, rt): δ 7.29 (m, 8H, C6H5 ortho), 7.01 (m, 12H, C6H5 para and C6H5 meta), 6.85 (d, 4H, α-CH, 3JHH = 5.0 Hz), 6.73 (d, 4H, β-CH, 3JHH = 5.0 Hz), 5.23 (dd, 2H, SiH, 3JPH = 11, 26 Hz, 2JPtH = 15 Hz, 1JSiH = 179 Hz), 1.78 (app d, 4H, CH2, 2JPH = 17 Hz). 13C{1H} NMR (126 MHz, C6D6, rt): δ 143.4 (Cq-Si), 136.9 (αCq), 133.4 (C6H5 ortho), 131.2 (m, 3JPC = 22 Hz, C6H5 ipso), 130.4 (αCH), 128.4 (C6H5 meta), 122.7 (β-CH), 28.5 (m, CH2); the C6H5 para signal is overlapped. 31P{1H} NMR (202 MHz, C6D6, rt): δ 59.2 (1JPtP = 1678 Hz). 29Si{1H} NMR (99 MHz, C6D6, rt): δ −23.1 (2JPSi = 4.2, 144 Hz); the JPtSi value was not estimated due to low intensity. Preparation of [{Pt(dppe)}2(μ-DTS)2] (4). A toluene solution (1 mL) of 1 (25 mg, 0.026 mmol) was stirred at 60 °C for 5 days to produce a red solution. The solvent was removed under reduced pressure. The resulting material was washed with hexane (2 mL × 3) and dried in vacuo to give 4 as an orange solid (5 mg, 24%). The 1H NMR spectrum of the mixture after heating for 102 h displayed the  CH signals of 3 and 4 with the intensities in 1.0:1.8 ratio. The crystals of 4, suitable for X-ray measurement, were obtained from recrystallization of the product from the C6D6 solution. HRMS (ESI) cacld for C68H56P4Pt2S4Si2 [M]2+ = 785.0519, found m/z = 785.0534. 1H NMR (500 MHz, C6D6, rt): δ 7.21 (d, 4H, α-CH, 3JHH = 4.5 Hz), 7.13 (app t, 16H, C6H5 ortho, 3JHH = 8 Hz), 7.00 (t, 8H, C6H5 para, 3JHH = 7 Hz), 6.94 (t, 16H, C6H5 meta, 3JHH = 7 Hz), 6.63 (d, 4H, β-CH, 3JHH = 4.5 Hz), 1.54 (d, 8H, CH2, 3JPH = 17 Hz). 13C{1H} NMR (126 MHz, C6D6, rt): 157.1 (Cq-Si), 142.3 (α-Cq), 133.7 (m, C6H5 ipso, 3JPC = 19 Hz), 132.8 (m, C6H5 ortho, 4JPC = 6 Hz), 130.7 (α-CH), 129.0 (C6H5 para), 30.4 (m, CH2, 1JPC = 23 Hz). 31P{1H} NMR (161 MHz, C6D6, rt): δ 60.7 (1JPtP = 1500 Hz, 3JPtP = 186 Hz, 4 JPP = 24 Hz, 2JSiP = 476 Hz). Alternative Preparation of 4. To a toluene solution (8 mL) of [Pt(PCy3)2] (115 mg, 0.15 mmol) were added an equimolar amount of DPPE (61 mg, 0.15 mmol) and DTSH2 (30 mg, 0.15 mmol). The reaction mixture was stirred at 60 °C for 45 h to produce a red solution. The solvent was removed under reduced pressure to give a solid, which was washed with hexane (4 mL × 3) and dried in vacuo to give 4 as a red solid (35 mg, 30%). X-ray Crystal Structure Analyses. Single crystals of 2 and 4 suitable for X-ray diffraction were mounted on MicroMounts (MiTeGen). The crystallographic data were collected on a Bruker SMART APEXII ULTRA/CCD diffractometer for 2 or a Rigaku Saturn CCD area detector for 4 equipped with monochromated Mo Kα radiation (λ = 0.71073 Å) at 113 or 90 K, respectively. Calculations were carried out using the program package APEXII or Crystal Structure for Windows. The positional and thermal parameters of nonhydrogen atoms were refined anisotropically on F2 by the full-matrix least-squares method using SHELXL-2014. Hydrogen atoms, except

Preparation of 4,4-Dihydrodithienosilole (DTSH2). To an ether solution (30 mL) of 3,3′-dibromo-2,2′-bithiophene (2.52 g, 7.78 mmol), cooled to −78 °C, was dropwise added 9.69 mL of nBuLi (1.61 M in hexane, 15.6 mmol). The white suspension mixture was stirred at the same temperature with stirring for 2 h and then dropwise added to the THF solution (5 mL) of H2SiCl2 (934 mg, 9.25 mmol). The reaction mixture was allowed to warm to room temperature overnight and then was quenched with aqueous NH4Cl solution. The crude product was extracted with Et2O and dried over anhydrous Na2SO4. The solution was concentrated under reduced pressure. The residue was distilled under reduced pressure, giving pure DTSH2 as colorless oil (1.30 g, 86%). Anal. Calcd for C8H6S2Si: C, 49.44; H, 3.11. Found; C, 49.04; H, 3.15. 1H NMR (500 MHz, C6D6, rt): δ 6.77 (d, 2H, αCH, 3JHH = 4.5 Hz), 6.71 (d, 2H, β-CH, 3JHH = 4.5 Hz), 4.53 (s, 2H, SiH, 1JSiH = 215 Hz). 13C{1H} NMR (126 MHz, C6D6, rt): δ 151.3 (Cq-Si), 135.0 (α-Cq), 129.8 (α-CH), 125.7 (β-CH). 29Si{1H} NMR (99 MHz, C6D6, rt): δ −56.0. IR (KBr): 2152 cm−1 (νSiH). Preparation of [Pt(DTSH)2(dppe)] (1). To a toluene solution (8 mL) of [Pt(PCy3)2] (153 mg, 0.20 mmol) was added an equimolar amount of DPPE (80 mg, 0.20 mmol) and two equimolar amounts of DTSH2 (78 mg, 0.40 mmol). The reaction mixture was stirred at room temperature for 23 h to produce a yellow solution. The solvent was removed under reduced pressure to give a solid, which was washed with hexane (4 mL × 3) and dried in vacuo to give 1 as a yellow solid (83 mg, 42%). Anal. Calcd for C42H34P2PtS4Si2 + C4H8O: C, 52.51; H, 4.02. Found; C, 52.22; H, 3.68. 1H NMR (500 MHz, C6D6, rt): δ 7.26 (m, 8H, C6H5 ortho), 7.02 (d, 4H, α-CH, 3JHH = 4.5 Hz), 6.99 (m, 4H, C6H5 para), 6.94 (m, 8H, C6H5 meta), 6.71 (d, 4H, β-CH, 3JHH = 4.5 Hz), 6.33 (app t, 2H, SiH, 3JPH = 7.0 Hz, 2JPtH = 77 Hz, 1JSiH = 187 Hz), 1.52 (d, 4H, CH2, 2JPH = 18.5 Hz). 13C{1H} NMR (126 MHz, C6D6, rt): δ 147.3 (Cq-Si), 132.7 (m, C6H5 ipso, 3JPC = 13 Hz), 131.0 (α-CH or α-Cq), 130.5 (α-Cq or α-CH), 122.8 (β-CH), 31.1 (m, CH2); other C6H5 signals were overlapped with solvent signals. 31 1 P{ H} NMR (202 MHz, C6D6, rt): δ 59.8 (1JPtP = 1727 Hz). 29 Si{1H} NMR (99 MHz, THF-d8, rt): δ −25.5 (dd, 2JPSi = 14, 152 Hz). The JPtSi value was not estimated due to low intensity. IR (KBr): 2048 cm−1 (νSiH). Pt-Catalyzed Preparation of 2. To a toluene solution (1 mL) of DTSH2 (206 mg, 1.1 mmol) was added 5 mol % 1 (52 mg, 53 μmol). The reaction mixture was stirred at 90 °C for 20 h to produce an orange solution. The solvent was removed under reduced pressure. The resulting material was washed with MeCN (4 mL × 3) and dried in vacuo to afford disilane 2 as a white solid (157 mg, 77%). The mixture did not contain any trans isomers. Pt(0) complex (5 mol %), prepared in situ from the reaction of [Pt(PCy3)2] (32 mg, 42 μmol) and DPPE (17 mg, 43 μmol), is also available for the catalytic dimerization of 1 (165 mg, 0.85 mmol) in toluene at 90 °C for 20 h, yielding 2 in 69% yield (113 mg, 0.29 mmol). Anal. Calcd for C8H6S2Si: C, 49.70; H, 2.61. Found; C, 49.90; H, 2.94. 1H NMR (500 MHz, C6D6, rt): δ 6.94 (d, 2H, α-CH, 3J = 5.0 Hz), 6.60 (d, 2H, β-CH, 3 J = 5.0 Hz), 4.98 (s, 2H, SiH, 1JSiH = 214 Hz). 13C{1H} NMR (126 MHz, C6D6, rt): δ 147.1 (Cq-Si), 134.3 (α-CH), 124.9 (α-Cq), 124.0 (β-CH). 29Si{1H} NMR (99 MHz, C6D6, rt): δ −70.1. IR (KBr): 2140 cm−1 (νSiH). Ni-Catalyzed Preparation of 2. To a toluene solution (1 mL) of DTSH2 (98 mg, 0.50 mmol) was added 1 mol % [Ni(PPh3)4] (5.6 mg, 5.0 μmol). The reaction mixture was stirred at room temperature for 14 h to produce a brown solution. The solvent was removed under reduced pressure. The resulting material was washed with acetonitrile (2 mL × 3) and dried in vacuo to afford 2 as a white solid (33 mg, 34%). Preparation of 2,6-Bis(trimethylsilyl)-4,4-dihydrodithienosilole (DTSH2-SiMe3). The preparation of DTSH2-SiMe3 was similar to that of DTSH2. To the ether solution (3 mL) of H2SiCl2 (440 mg, 4.36 mmol) was added the dilithio compound prepared by 3,3′dibromo-5,5′-bis(trimethylsilyl)-2,2′-bithiophene (1.02 g, 2.18 mmol) and 2.73 mL of nBuLi (1.60 M in hexane, 4.36 mmol), giving pure DTSH2-SiMe3 as colorless oil (674 mg, 91%). HRMS (ESI) calcd for C14H23S2Si3 [M]+ = 339.0543, found m/z = 339.0538. 1H NMR (500 MHz, C6D6, rt): δ 7.06 (s, 2H, CH), 4.73 (s, 2H, SiH, 1JSiH = 213 Hz), E

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for Si−H hydrogens of 2, were placed at calculated positions and refined with a riding mode on their corresponding carbon atoms. The CCDC 1532277 (2) and 1532278 (4) contain the supplementary crystallographic data for this paper.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.7b00177. NMR (1−4) and optical (DTSH2 and 2) spectra (PDF) Cartesian coordinates of 1, 2, 2′, and 3 (PDF) Accession Codes

CCDC 1532277 and 1532278 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Kohtaro Osakada: 0000-0003-0538-9978 Joji Ohshita: 0000-0002-5401-514X Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by a Grant-in-Aid for Scientific Research on Innovative Areas New Polymeric Materials Based on Element-Blocks (No. 2401) (JSPS KAKENHI Grant Nos. 24102005 and 15H00725) and Scientific Research (C) (No. 16K05789), from Ministry of Education, Culture, Sports, Science, and Technology, Japan. We thank our colleagues in the Center for Advanced Materials Analysis, Technical Department, Tokyo Institute of Technology, for elemental analysis and ESI-MS measurements.

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REFERENCES

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